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    Re: Digital Sextant
    From: Vic Fraenckel
    Date: 2002 Apr 2, 08:41 -0500

    Dan Allen wrote:
    | I wonder what kind of silicon sensors exist that act as artificial
    horizons,
    | and what kind measure angles, and how accurately?  The digital compasses
    | recently referred to are accurate to 2 degrees.  For a sextant the angle
    | needs to be measured to a few seconds of arc to be competitive.
    
    In discussing the Digital Sextant, one must NOT confuse a digital compass
    with the method of measuring altitude. A sextant is NOT used to measure
    azimuth so to quote the accuracy of a digital compass module as an argument
    against the possibility of building a Digital Sextant clouds the issue. I
    have personally used digital optical encoders that can measure an angle to
    360/4096 degrees = 0.088 degrees = 5.27 minutes. The encoder resolves 360
    degrees into 4096 counts. While this does NOT come close to what would be
    needed to make the Digital Sextant, it is a device I am familiar with. There
    exists encoders that have even higher resolution.
    
    There also exists a integrated circuit device (Analog Devices ADXL202) which
    can measure it's own relationship to the the earth's gravitational field and
    who's output is a measure of the angles it makes with the gravitational
    field in two axes.  I have used this device as well..
    
    I have interfaced both devices to a microcontroller with ease and made
    useful measurements with them. Perhaps a Digital Sextant is not so far
    fetched after all!
    
    Vic
    ________________________________________________________
    
    Victor Fraenckel - The Windman                 vfraenc1{at}nycap.rr.com
    KC2GUI                                                      www.windsway.com
    
          Home of the WindReader Electronic Theodolite
                                   Read the WIND
    
    
    

       
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